Booster-type gas compressor

ABSTRACT

In a booster-type gas compressor, an electric motor in a motor case drives a crank shaft integrally connected to a driving shaft. The crank shaft is coupled to a piston rod extending perpendicular to the crank shaft and having a piston at the upper end. Rotation of the crank shaft allows the piston up and down. A compressed gas from a compressed-gas flow path is fed to a compressing chamber above the piston and further compressed by the piston. A bypath conduit connects the compressed-gas flow path to the motor case to keep pressure in the crank case to more than atmospheric pressure.

BACKGROUND OF THE INVENTION

The present invention relates to a booster-type gas compressor in whicha compressed gas is further compressed by a reciprocating piston.

As shown in FIG. 4, a suction valve 23 is provided at one side of a topwall 22 of a cylinder 21 and a discharge valve 24 is provided at theother side of the top wall 22. Above the suction valve 23 and thedischarge valve 24, there are a suction chamber 26 having an inlet 25and a discharge chamber 28 having an outlet 27 respectively. Under thecylinder 21, a crank shaft 31 integrally formed with a driving shaft 30in a crank case 29 is provided. The driving shaft 30 is driven by anelectric motor 34 in a motor case 33 mounted to a side wall 29 a of thecrank case 29 so that a gas may pass through. A piston 39 is moved upand down in a cylinder 21 via a piston rod 35 by the crank shaft 31formed with the driving shaft 30 to compress a gas such as N₂ introducedin a compressing chamber above the piston 36 via the suction valve 23and to discharge it from the discharge valve 24 and outlet 27.

In such a reciprocating-piston-type gas compressor, with reciprocatingmotion of the piston 36, a compressed gas in the compressing chamberabove the piston 36 in the cylinder 21 partially leaks through aroundthe piston 36 into the crank case 29.

The compressed gas in the crank case 29 Is partially discharged from anair hole 38 of the crank case 29 to produce loss of energy. Leak of atoxic gas causes air pollution.

Furthermore, in case that such a reciprocating-piston-type gascompressor comprises a booster-type gas compressor sucking a compressedgas and compressing it to higher pressure, in a suction step ofrestarting or unloading operation, the compressing chamber becomesdecompression condition in which a atmospheric pressure gas from an airhole 38 of the crank case 29 flows through around the piston 36 to thecompressing chamber above the piston 36 and is mixed in a gas from thesuction hole 25 to render density lowered.

To cool the electric motor 34, a ventilating hole 39 is formed in theelectric motor case 33 or a fan is mounted to the driving shaft 30 toachieve forcing cooling. Thus, the electric motor 34 cannot becompletely sealed to render noise leaked or dusts, and solid ingredientsin external air are likely to remain in the electric motor 34 or motorcase 33.

Furthermore, in such a booster-type gas compressor, atmospheric pressureremains in the crank case 29. So, owing to pressure difference above andunder the piston 36, torque variation in one rotation becomes greater toincrease an electric current of the electric motor 34 directly mountedto the crank case 29 to speed up damages on the outer circumferentialsurface of the piston 36, a piston ring, the driving shaft 30, bearings41,42 of the crank shaft 31 and a seal of a sliding portion.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a booster-type gascompressor comprising a reciprocating piston, pressure difference beingreduced between a compressing chamber above the piston and a crank caseunder the piston thereby preventing wear of each part and unsmoothnessof the operation.

BRIEF DESCRIPTION OF THE DRAWINGS

The features and advantages of the invention will become more apparentfrom the following description with respect to embodiments as shown inaccompanying drawings wherein:

FIG. 1 is a vertical sectional view of the first embodiment of abooster-type gas compressor according to the present invention;

FIG. 2 is a vertical sectional view of the second embodiment of abooster-type gas compressor according to the present invention;

FIG. 3 is a vertical sectional view of the third embodiment of abooster-type gas compressor according to the present invention; and

FIG. 4 is a vertical sectional view of a known booster-type gascompressor

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 shows the first embodiment of a booster-type gas compressoraccording to the present invention.

The basic structure of the booster-type gas compressor is not sodifferent from that in FIG. 4. The same numerals are allotted to thesame members. Its description is omitted and only differences aredescribed.

In FIG. 1, there is no air hole 38 communicating external air and acompressed-gas introducing hole 11 is formed in an electric motor case36 instead of a ventilating hole.

A compressed-gas feeding path 37 is connected to a compressed-gasintroducing hole 11 via a bypath conduit 14 comprising a check valve 12that closes towards the compressed-gas feeding path 37 and opens in anopposite direction and a pressure regulator 13 such as apressure-regulating valve or a pressure reducing valve.

By opening a valve (not shown), a compressed gas is fed into a suctionchamber 26 and partially introduced into the crank case 29 via thebypath conduit 14 comprising the check valve 12 and the pressureregulator 13, the compressed-gas introducing hole 11. a motor case 33and a communicating hole 32 to let the inside of the crank case 29compressed to more than atmospheric pressure.

The compressed gas in the compressed-gas feeding path 37 is partiallyfed into the crank case 29, so that gas pressure in the crank case 29becomes more than atmospheric pressure different from a known device.

Thus, difference in pressure between a compressing chamber above apiston 36 in a cylinder 21 and the inside of the crank case 29 becomessmaller than that in a known device, thereby preventing sliding of thepiston 36 from lacking smoothness and preventing each of the bearings41,42 and preventing a seal from reducing their lives or producinglooseness caused by unequal force.

By the pressure regulator 13, pressure of a compressed gas in the crankcase 29 is regulated, so that pressure difference from a compressionchamber above the piston 37 is regulated as soon as possible therebyachieving stable performance.

As shown in FIG. 2, a pressure regulator 15 may be directly joined tothe crank case. The pressure regulator 15 may be a reserve tankcomprising a pressure-regulating valve and a check valve therebyachieving similar advantage to that in FIG. 1.

In FIG. 3, a compressed-gas feeding path 37 is connected to acompressed-gas introducing hole 11 of a motor case 33 via a bypathconduit 14 comprising a check valve 12 that closes towards thecompressed-gas feeding path 37 and opens in an opposite direction. Apressure regulator 13 is provided on the compressed-gas feeding path 37between the bypath conduit 14 and a suction valve 23 thereby achievingsimilar advantage to that in FIG. 1.

The foregoing merely relates to embodiments of the invention. Variouschanges and modifications may be made by a person skilled in the artwithout departing from the scope of claims wherein:

1. A booster-type gas compressor comprising: a crank case; a crank shaftin the crank case; a driving shaft integrally connected to the crankshaft; a motor case; an electric motor joined to the driving shaft todrive the driving shaft in the motor case; a cylinder; a piston in thecylinder; a piston rod joined to the piston at an upper end and to thecrank shaft at a lower end; a compressed-gas flow path that feeds acompressed gas into a compressing chamber above the piston to furthercompress the gas; and a bypath conduit that connects the compressed-gasflow path to the crank case to keep pressure in the crank case to morethan atmospheric pressure.
 2. A compressed of claim 1 further comprisinga pressure regulator at the bypath conduit.
 3. A compressor of claim 1further comprising a pressure regulator at the crank case.
 4. Acompressor of claim 1 further comprising a pressure regulator at thecompressed-gas flow path between the bypath conduit and the cylinder.